THIS invention relates to a rotary distribution apparatus which incorporates interstage pumps.
WO 2004/029490 describes a rotary distribution apparatus (RDA) which allow batch processes to be conducted with an efficiency approaching that of continuous operation. The apparatus may for instance be used in ion exchange and chromatographic separation in, for example, the processing of sugar juice in a sugar extraction plant.
FIG. 1 illustrates a known RDA according to WO 2004/029490. The apparatus 1 has a stationary, cylindrical, central core 2 into which fixed feed and product pipes 3 extend. A set of annular fluid distribution chambers (not visible in FIG. 1) are defined between the core 2 and an outer shell or barrel 4 which rotates around the core with, in practice, one distribution chamber provided per feed or product stream. Pipes 5 which rotate with the shell 4 are connected between selected distribution chambers and selected ports in an indexing disc 6 which rotates with the shell. The disc 6 rotates relative to a stationary indexing disc 7. As the disc 6 rotates relative to the disc 7 different process streams fed to the former disc through the pipes 5 are introduced to fixed ports in the latter disc which in turn feed the streams selectively to process chambers, typically ion-exchange or chromatographic separation chambers in the case of sugar extraction, through pipes 8. Fluid streams which return from the process chambers follow similar routes in reverse and are eventually discharged from the apparatus through relevant ones of the fixed pipes 3.
In a chromatographic separation application, by way of example, the process fluids are required to pass through several process chambers containing resin, typically for regeneration of the resin. In some zones of the distribution system, the fluid viscosity can be quite high with the result that the associated pressure drops can be significant. This generally requires careful design of the pipes and associated pumping apparatus.
In a conventional simulated moving bed chromatographic separation system, as described for instance in U.S. Pat. No. 5,122,275 to Rasche (assigned to A.E Staley Manufacturing Company), the separation columns and necessary pumps are fixed in position while the actual separation profile moves from column to column. As the profile moves through the columns the fluid viscosities and hence the pumping duties vary significantly, which means that the capacities of the pumps must be carefully selected to handle the full range of fluid potential flows and pressure variations at all points in the cycle.
Where an RDA as referred to above is used the separation columns are fixed and an approach might be to provide an interstage pump at each column. This potential solution is however considered to be rather inefficient, as pumps may not be required at all in zones where the fluids have low viscosities. If, on the other hand, a smaller number of larger pumps is used, the pressure drops become more significant and at least some of the column chambers need to be of robust construction to withstand the applied pressures.
An added difficulty with such a solution is that the pumps would see different duties and have different flow setpoints after each index in the processing cycle.
These factors combine to make the overall pump control strategy very complex. This is a problem which the present invention seeks to overcome.